1. Field of the Invention
This invention relates in general to electric submersible well pumps. More specifically, this invention relates to submersible well pumps that have an impeller configuration designed for high viscosity fluids and operate at high rotative speeds.
2. Description of the Prior Art
Traditionally the use of electric submersible pumps (ESP's) in low flow viscous crude pumping applications has been limited because of low efficiencies inherent with low capacity centrifugal pumps handling viscous fluids. Low efficiencies result from disk friction losses caused by a layer of viscous fluid adhering to the walls of both rotating and stationary components within the pump impeller and diffuser. Viscous fluids are considered herein to be fluids with a viscosity greater than 500 centipoise.
Others have made and used ESP's to pump viscous materials. However, most of these attempts have involved either modifying the material to be pumped or controlling the output of the pump motors with additional equipment to assist in the low flow conditions typical of pumping high viscous materials from wells.
Others have attempted to pump high viscous materials by simply lowering the viscosity of the material, as opposed to trying to modify the pump or motor to accommodate the high viscous materials. U.S. Pat. Ser. No. 6,006,837 to Breit (hereinafter “Breit Patent”), U.S. Pat. Ser. No. 4,721,436 to Lepert (hereinafter “Lepert Patent”), and U.S. Pat. Ser. No. 4,832,127 to Thomas et al. (hereinafter “Thomas Patent”) are three such examples of this type of invention.
In the Breit Patent, the viscous fluids that are being pumped are heated in order to lower the viscosity of the fluid being pumped. The Lepert Patent discloses a process for pumping viscous materials by mixing the high viscosity materials with low viscosity materials with the use of a turbine-machine that consists of a turbine and a pump, separating the mixture, and recirculating the low viscosity materials for reuse. The Thomas Patent discloses a process for pumping viscous materials by mixing the high viscosity oil with water to lower the viscosity and then pump the material by conventional methods once the viscosity is suitable for pumping. Each of these references alters the fluid being pumped, without trying to modify the pump or motor to accommodate the fluid being pumped.
A need exists for an ESP and method of pumping high viscosity materials while maintaining pumping efficiencies, without altering the material being pumped or trying to maintain torque or rpm levels in a pump motor without the use of additional equipment. Ideally, such a system should be capable of being adapted to the specific applications and also be able to be used on existing equipment with minimal modification.